It is widely recognized, on the basis of both clinical and pathological evidence, that the proximal cause of the nearly one million myocardial infarctions in the United States each year is almost always the formation of intracoronary thrombus. The precipitating event leading to the formation of a clot is typically rupture or fracture of intracoronary plaque--an event that destroys the integrity of the endothelium and exposes thrombogenic subintimal material to luminal blood flow.
At present, clinical study of coronary atherosclerosis relies almost entirely on coronary angiography in which radiopaque contrast agent is introduced into each of the coronary arteries and observed by X-ray as it fills the lumen of the artery. Although the procedure defines, in silhouette, the borders of the coronary lumen, making it possible to measure coronary obstruction, it yields no information on the properties of the obstructing plaque, its fragility or susceptibility to rupture, nor on the properties of the local coronary blood flow, a major determinant of the future growth and composition of the underlying plaque.